EJB Mapping

Source: http://trailblazer.demo.jboss.com/EJB3Trail/persistence/config/

Injecting an EntityManager from a specific context

As we can see, the persistence.xml file in the JAR file can define multiple persistence contexts with different names. To obtain an EntityManager from a named persistence context, you just need to specify the name in the unitName attribute of the @PersistenceContext annotation. The following example injects the ejb3trail persistence context to the EntityManager.

@PersistenceContext(unitName="ejb3trail")

EntityManager em;

You can omit the unitName attribute if the following conditions are met:

* You only have one persistence context defined in the persistence.xml file in the entire application.

* You are using a scoped classloader for the application.

The second item probably needs more explanation. In a web application deployed in an EAR file, that means you need a jboss-app.xml file in the EAR file's META-INF directory. The file can specify an arbitrary name for the classloader. Here is an example:

<jboss-app>

<loader-repository>

trailblazer:app=ejb3

</loader-repository>

</jboss-app>

If you do not have a scoped classloader for the application, all the persistence contexts defined in the applications would be globally available in the entire server, and the @PersistenceContext injection look for an EntityManager in the global context as well. That allows you to use persistence context defined outside of your own application. But you also have to explicitly specify the persistence context name via the unitName attribute.

- Saish

Saisha at 2007-7-8 23:59:07 >

You will need some kind of data access object (DAO) to interact with your JPA entities. (Alternatively, you can have your stateless session bean directly interact with your JPA entities). In any case, you will need a PersistenceContext.You probably already have this coded as:

@PersistenceContext

EntityManager em;

All you want to change is to supply the name of the JNDI data source that you defined earlier by creating a [name of data source]-ds.xml file and placing it in JBoss's /server/default/deploy directory. There are already several -ds.xml files in that directory that you can model your data source after (ideally, find the one named after your database, duplicate the file and rename it, then custom edit it). Here is the change in your code:

@PersistenceContext(unitName="myOtherDataSource")

EntityManager em;

You would therefore need to create myOtherDataSource.ds. I have included the oracle-ds.xml that ships with JBoss. You can edit it for your own settings. Make sure the JNDI name you reference in your code matches the one you use in the file. Good luck!

<datasources>

<local-tx-datasource>

<!-- THIS IS WHAT MUST MATCH THE JNDI NAME YOU USE IN YOUR EJB'S -->

<jndi-name>myOtherDataSource</jndi-name>

<connection-url>jdbc:oracle:thin:@localhost:1521:TEST</connection-url>

<driver-class>oracle.jdbc.driver.OracleDriver</driver-class>

<user-name>foo</user-name>

<password>bar</password>

<valid-connection-checker-class-name>org.jboss.resource.adapter.jdbc.vendor.OracleValidConnectionChecker</valid-connection-checker-class-name>

<exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.OracleExceptionSorter</exception-sorter-class-name>

<metadata>

<type-mapping>Oracle9i</type-mapping>

</metadata>

</local-tx-datasource>

</datasources>

[

- Saish

Saisha at 2007-7-8 23:59:07 >

Saish,

You have the patience of a saint! Hehe - thanks, I understand the above and now where the reference fits in to the EJB... although have one (final I hope) question on the matter..

My current code is:

public abstract class ExampleEntityBean implements EntityBean{

private transient EntityContext ec;

.... methods

}

& it works fine, can be looked up, etc.

If I place a @PersistenceContext(unitName="xxxxxx") above it, Eclipse says it cant compile with annotations unless source level is set to 5:0?

:-S

I'm nearly there, honestly! :-) Many thanks!

Terry

not_terrya at 2007-7-8 23:59:07 >

Saish,

The comment regarding abstract scared me - I have spent a fair bit learning it this way, and it's out of date! :-)

I got Eclipse to compile with your advice, sadly it appears still to be looking in to the wrong database.

@PersistenceContext(unitName="java:TestDB")

private EntityContext ec;

java:TestDB is the ref I use when making a direct connection to the DB, pulling out that DS - so I know thats correct - and it also matches the -TestDB-ds.xml file.

If you have any other suggestions that would be fantastic - but can understand if you're sick of this now!

Terry

not_terrya at 2007-7-8 23:59:07 >

Hey there,

OK Let's try and sort this out by giving everything! :-)

I have:

My class:

public abstract class ContentBean implements EntityBean{

@PersistenceContext(unitName="TestDB")

private EntityContext ec;

public ContentBean(){ }

public Integer ejbCreate(Integer contentid) throws CreateException {

return contentid;

}

...other methods

}

* Home & Remote classes are ok.

* I've left abstract in for now, as I can't see how the rest would work - going to get this up and then move over to EJB 3.0.

XML Files:

xxx.jar/META-INF/ejb-jar.xml

<ejb-jar >

<description>EJB Examples</description>

<display-name>EJB Examples</display-name>

<enterprise-beans>

<entity>

<description>ContentView</description>

<ejb-name>ContentView</ejb-name>

<home>p.ContentHome</home>

<remote>p.ContentRemote</remote>

<ejb-class>p.ContentBean</ejb-class>

<persistence-type>Container</persistence-type>

<prim-key-class>java.lang.Integer</prim-key-class>

<primkey-field>contentid</primkey-field>

<abstract-schema-name>cview</abstract-schema-name>

<reentrant>False</reentrant>

<cmp-field><field-name>contentid</field-name></cmp-field>

<cmp-field><field-name>contenttitle</field-name></cmp-field>

</entity>

</enterprise-beans>

xxx.jar/META-INF/persistence.xml ( HUGE thanks for this one matie - I found a great URL about it too at http://trailblazer.demo.jboss.com/EJB3Trail/persistence/config/ for any newbies like me reading this )

<persistence>

<persistence-unit name="TestDB">

<jta-data-source>java:/TestDB</jta-data-source>

<properties>

</properties>

</persistence-unit>

</persistence>

*I have tried combinations of TestDB and java:TestDB for the data-source

jboss/.../deploy/TestDB-ds.xml

<datasources>

<local-tx-datasource>

<jndi-name>TestDB</jndi-name>

.....[details of my other db]

</datasources>

* I can manually connect to this DB via the DS using a Context look up so believe this is ok too.

test.jsp:

javax.naming.Context ctx = new javax.naming.InitialContext();

p.ContentHome home = (p.ContentHome) javax.rmi.PortableRemoteObject.narrow(ctx.lookup("ContentView"),p.ContentHome.class);

p.ContentRemote he = home.findByPrimaryKey(new Integer( 1 ));

out.println("Hello");

out.println("Content ID: " + he.getContentid());

out.println("title: " + he.getContenttitle());

Phew! Ok that should give a full picture of what I'm doing - if you could take a look that'd be fantastic. Also; how can I give you more stars? It says I have 20 but has limited me to allocating 10!?! :-(

Thanks,

Terry

not_terrya at 2007-7-8 23:59:07 >